ADAMTS-13 is a zinc-metalloprotease belonging to ADAMTS (a disintegrin-like domain, and metalloprotease, with thrombospondin type 1 motif) family and specifically cleaves von Willebrand factor (VWF) at Tyr1605-Met1606, which corresponds to 842-843 after cleavage of a preprosequence (VWF cleavage enzyme: VWF-Cleaving Protease, VWF-CP)(see e.g. Non-patent reference 1). ADAMTS-13 is known to be an activity modulation factor of VWF that is an important factor of platelet aggregation. VWF released through stimulation or circulating in blood is important in forming platelet thrombus because it plays a role as a collaboration with collagen on platelet adhesion and agglutination in the subendothelial tissue of a damaged vascular wall (e.g. see Non-patent reference 2).
It is considered that VWF is subjected to conformational change by intravascular shear force in blood circulation to thereby expose A2 domain, and Tyr1605-Met1606 therein, ADAMTS-13 cleavage site, is rapidly hydrolyzed by ADAMTS-13. Anderson et al. evaluated a catalytic efficiency of ADAMTS-13 using as a substrate VWF previously subjected to guanidinium hydrochloride to induce the conformational change (see e.g. Non-patent reference 3). The result showed that kcat was up to 0.83 min−1 and kcat/Km was 55 μM−1 min−1, which are lower than those of the other enzymes of a coagulation system to natural high molecular weight substrates, indicating that ADAMTS-13 has a lower enzymatic activity.
Thrombotic thrombocytopenic purpura (hereinafter also referred to as “TTP”) caused by a reduced activity of ADAMTS-13 is classified into a congenital TTP and an acquired TTP. The congenital TTP is hereditary and caused by a molecular abnormality of ADAMTS-13 (also called Upshow Schulmann syndrome (USS)) and the acquired TTP is positive in a neutralizing autoantibody to ADAMTS-13. While a plasma transfusion is currently conducted to supplement ADAMTS-13 for treating the congenital TTP, it is desired that an ADAMTS-13 concentrate or a recombinant formulation is alternatively used for said treating in future. Moreover, a plasmapheresis is generally conducted to both remove the neutralizing antibody and to supplement ADAMTS-13 for treating the acquired TTP.
It has often reported that the molecular abnormality of ADAMTS-13 is found in patients with congenital TTP (USS) wherein a missense and/or nonsense mutation is found throughout the molecule. However, the pathogenesis of TTP starting in adult are also found, suggesting that possibly the congenital reduced ADAMTS-13 is not the only trigger of the pathogenesis of TTP. Considering that there are cases of the pathogenesis of congenital TTP during a pregnancy (VWF in blood may increase to 300% of the normal value during late pregnancy), the systemic platelet thrombus formation arising from TTP may be caused by the increased VWF in blood induced by the second trigger such as an environment factor or a genetic factor in addition to the reduced ADAMTS-13 in blood. Indeed, the present inventors have found that a re-event rate of acute myocardial infarction (hereinafter also referred to as “AMI”) within 1 year is significantly high when the ratio between VWF and ADAMTS-13 in blood (VWF/ADAMTS-13) after 24 hours of the onset of AMI exceeds a certain value (see e.g. Patent reference 1).
In addition, an ADAMTS-13 antigen level in plasma of patients with thrombotic disease, including disseminated intravascular coagulation (DIC), hemolytic-uremic syndrome (HUS), deep vein thrombosis (DVT), TTP, pulmonary embolism, cerebral infarction and systemic lupus erythematosus (SLE), is significantly reduced compared to healthy adult (see e.g. Patent reference 2), wherein an ADAMTS-13 antigen level is measured with sandwich ELISA using a monoclonal antibody. Moreover, with respect to DIC associated with septicemia, it was shown that patients having ADAMTS-13 blood level of less than 20% is significantly likely to develop nephropathy as compared to patients having ADAMTS-13 blood level of 20% or more (see e.g. Non-patent reference 4).
Meanwhile, endothelial cells stimulated by inflammatory cytokine, IL-8 and/or TNF-α, induce a release of unusually large (UL) VWF that has a larger multimer structure than normal. There is also an experimental result that IL-6 inhibits a VWF cleaving activity of ADSAMTS-13 under a shear stress of blood Flow (ex vivo). Therefore, it is suggested that there is an association between inflammation and thrombus formation (see e.g. Non-patent reference 5).
In addition, it is reported that ciga toxin which causes HUS stimulates vascular endothelial cells to promote ULVWF release and inhibits the activity of ADAMTS-13. It seems possible that HUS is improved by administering ADAMTS-13 to patients with HUS (see e.g. Non-patent reference 6). Thus, when the disease as stated above may be aggravated due to an imbalance involving the reduced ADAMTS-13 and the elevated VWF, administration of ADAMTS-13 may alleviate the condition of the disease.
ADAMTS-13 as previously described belongs to a metalloprotease group called ADAMTS family. ADAMTS-1 to -20 are known as a member of this family (ADAMTS-5 is identical to ADAMTS-11). ADAMTS-13 as well as the other members of ADAMTS family has a multidomain structure (FIG. 1). The amino acid sequence of ADAMTS-13 is encoded by a DNA which contains 4284 bases and ranges from a start codon ATG(Met) to a stop codon TGA. An ADAMTS-13 gene has 29 Exons on the chromosome 9q34 and 37 kb in full-length. It is revealed via the gene sequencing of ADAMTS-13 protein that ADAMTS-13 protein has 1427 amino acid residues in the precursor thereof and 10 asparagine-linked glycosylation potential sites and is a large single-strand glycoprotein (Patent reference 4).
In a process of biosynthesis, a preprosequence of 74 residues is cleaved by a processing endoprotease Furin to provide a mature form containing 1353 amino acid residues. RQRR sequence (SEQ ID NO: 80), a cleaved motif of Furin, at the end of preprosequence is followed by a metalloprotease domain that contains a Reprolysin type zinc chelate domain comprising a consensus sequence HEXXHXXGXXHD (SEQ ID NO: 81). Then, via a disintegrin-like domain which is found in a snake venom metalloprotease, there follows the first Tsp1 motif (Tsp1-1) consisting of about 50 to 60 residues which is generally thought to be important for a molecular recognition and then a cysteine-rich domain containing one of a cell adherence motif, Arg-Gly-Asp (RGD) sequence. A spacer domain containing about 130 amino acid residues without cysteine residue then follows, and again Tsp1 motif is repeated (Tsp1-2 to Tsp1-8) followed by CUB 1 and 2 domains that have firstly been found in complement components C1r or C1s. These CUB domains are characteristic of ADAMTS-13 because among ADAMTS family only ADAMTS-13 has these domains. The present inventors have previously identified from the metalloprotease domain to spacer domain of ADAMTS-13 as domains essential for exerting an enzymatic activity or as an epitope for antibody neutralization (see e.g. Patent reference 3, and Non-patent references 7 and 8).    Patent reference 1: JP-A-2007-248395    Patent reference 2: WO2005/062054    Patent reference 3: WO2004/029242    Patent reference 4: WO2002/088366    Non-patent reference 1: Soejima, K., Mimura, N., Hirashima, M., Maeda, H., Hamamoto, T., Nakagaki, T. & Nozaki, C.: A novel human metalloprotease synthesized in the liver and secreted into the blood: possibly, the von Willebrand factor-cleaving protease? J. Biochem., 130: p. 475-480, 2001    Non-patent reference 2: Soejima, K. & Nakagaki, T.: Interplay between ADAMTS13 and von Willebrand factor in inherited and acquired thrombotic microangiopathies. Semin. Hematol., 42: p. 56-62, 2005    Non-patent reference 3: Anderson, P. J., Kokame, K. & Sadler, J. E.: Zinc and calcium ions cooperatively modulate ADAMTS13 activity. J. Biol. Chem., 281: p. 850-857, 2006    Non-patent reference 4: Ono, T., Mimuro, J., Madoiwa, S., Soejima, K., Kashiwakura, Y., Ishiwata, A., Takano, K., Ohmori, T. & Sakata, Y.: Severe secondary deficiency of von Willebrand factor-cleaving protease (ADAMTS13) in patients with sepsis-induced disseminated intravascular coagulation: its correlation with development of renal failure. Blood, 107: p. 528-534, 2006    Non-patent reference 5: Bernardo, A., Ball, C., Nolasco, L., Moake, J. F. & Dong, J. F.: Effects of inflammatory cytokines on the release and cleavage of the endothelial cell-derived ultralarge von Willebrand factor multimers under flow. Blood, 104: p. 100-106, 2004    Non-patent reference 6: Nolasco, L. H., Turner, N. A., Bernardo, A., Tao, Z., Cleary, T. G., Dong, J. F. & Moake, J. L.: Hemolytic uremic syndrome-associated Shiga toxins promote endothelial-cell secretion and impair ADAMTS13 cleavage of unusually large von Willebrand factor multimers. Blood, 106: p. 4199-4209, 2005    Non-patent reference 7: Soejima, K., Matsumoto, M., Kokame, K., Yagi, H., Ishizashi, H., Maeda, H., Nozaki, C., Miyata, T., Fujimura, Y. & Nakagaki, T.: ADAMTS-13 cysteine-rich/spacer domains are functionally essential for von Willebrand factor cleavage. Blood, 102: p. 3232-3237, 2003    Non-patent reference 8: Soejima, K., Nakamura, H., Hirashima, M., Morikawa, W., Nozaki, C. & Nakagaki, T.: Analysis on the molecular species and concentration of circulating ADAMTS13 in blood. J. Biochem., 139: p. 147-154, 2006